Typical turbo-molecular pumps such as those manufactured by BOC Edwards of Crawley, West Sussex, United Kingdom (“Edwards”) and Pfeiffer Vacuum Inc. of NH, USA (“Pfeiffer”) have a single high vacuum inlet at the top of the rotor stack designed to evacuate a single vacuum region.
Some turbo-molecular pumps also have inter-stage ports that allow for pumping of more than one vacuum region. For example, the Edwards EXT255H is a compound molecular pump with a high-vacuum stage and a drag stage (see U.S. Pat. No. 6,709,228B2 to Stuart). This configuration allows for pumping on two vacuum regions, one high vacuum and one low vacuum. However, an additional one of these pumps would be required to evacuate a second high vacuum region.
There are also “split flow” turbo-molecular pumps, such as the Edwards EXT200/200/30, which create a second high vacuum stage by placing a port in the side of the turbo-molecular section of the pump, at a distance of a few rotor blade heights downstream from the high vacuum inlet.
However, both the compound and split flow types of pumps increase the cost of the pumping system and require more space for the vacuum pumps.
There are some turbo-molecular pumps, such as the Pfeiffer TMH 262-020 YP, that have a support structure above the top rotor blades in the high vacuum inlet. This structure is used to support the rotor shaft bearing at the top of the rotor stack. The gap between the structure and the rotor blades is roughly one-half the width of the support. There is no provision to mate the support structure to the vacuum manifold to create multiple vacuum regions. Thus, this structure is only used as a support structure and does not result in the division of the turbo-molecular pump's high-vacuum inlet into more than one vacuum region for differential pumping.
The cost of the pumping system in instruments using a vacuum system can be a significant portion of the total cost of the instrument. The addition of another vacuum pump or the use of a more costly vacuum pump can be a significant cost disadvantage. It can also result in bulky and difficult to manage vacuum systems.
It would be desirable to provide a low cost and compact pumping system for pumping a differential vacuum between several vacuum chambers of a vacuum system.